Device for adjusting the stroke volume in a swash plate axial piston motor or pump

ABSTRACT

THE TILTING ANGLE OF A SWASH PLATE IN A FLUID PUMP OF MOTOR IS ADJUSTED BY A PISTON ARTICULTED TO THE PLATE AND POSITION CONTROLLED BY A SERVO VALVE WHICH, IN TURN, IS OPERATED BY A PLUNGER COUPLED TO THE SWASH PLATE BY A SINGLE CONTROL LEVER. THE CONNECTING LEVER IS CONNECTED TO SWASH PLATE AND PLUNGER SO THAT ONE OF THE CONNECTING POINTS CAN UNDERGO DIMENSIONAL MOTION IN RELATION TO THE RESPECTIVE OTHER ONE.

NOV. 9, 1971 KNAAK 3,618,472

DEVICE FOR ADJUSTING THE STROKE VOLUME IN A SWASH PLATE, AXIAL PISTONMOTOR OR PUMP Filed Feb. 9, 1970 2 Shoots-Shoot 1 Fig" 34 2a 41;, 40 44In ventor 1 4 naal JyKZwM NOV. 9, 1971 H KNAAK 3,618,472

DEVICE FOR ADJUSTING THE STROKE VOLUME IN A SWASH PLATE, AXIAL PISTONMOTOR OR PUMP Filed Feb. 9, 1970 2 Sheets-Shoot 2 a H F Flg- 2 I 2Inventor: H44; 1 /1446 @fiaa #4 6 United States Patent US. Cl. 91506 11Claims ABSTRACT OF THE DISCLOSURE The tilting angle of a swash plate ina fluid pump or motor is adjusted by a piston articulated to the plateand position controlled by a servo valve which, in turn, is operated bya plunger coupled to theswash plate y a single control lever. Theconnecting lever is connected to swash plate and plunger so that one ofthe connecting points can undergo three dimensional motion in relationto the respective other one.

The present invention relates to control device for infinite adjustmentof the stroke volume of swash plate fluid motors or pumps with axiallyoperating pistons. The invention relates particularly to improvements inarrange ments of a control piston, of feedback servo valve, of a swashplate tilt angle adjuster, and of linkage between them as well as forthe swash plate.

Upon varying the tilting angle of a swash plate, the point of connectionthereof to the tilt control device outlines a circle. Thus, it has beenfound necessary to employ at least two coupled levers as linkage to takeu this circular motion of adjustment. Aside from the construction beingexpensive, a plural member lever mechanism has the disadvantage thatplay in the several joints superimpose by addition, and the accuracy ofadjustment deteriorates accordingly. This is hardly tolerable, as pumpor motor adjustment requires usually great precision, otherwiseerroneous motion components of significant magnitude are included in thedrive and drive position output to be produced. The problem exists,therefore, to simplify the linkage between swash plate, adjustingmechanism, feedback structure and adjustment input, and particularly toreduce the number of levers, joints and linking points. Also, a compactdesign of the entire adjusting mechanism is highly desirable.

In accordance with one aspect of the invention in the preferredembodiment thereof, there is provided a control piston linked to theswash plate and position controlled by a servo valve, as the valvecontrols fluid passage to and from the piston chamber or cylinder of thecontrol piston, in dependence upon position of a control plunger. Theplunger is linked to the swash plate by means of a single control leverto obtain feedback which lever can pivotally move as if supported by anactual spherical bearing due to pivotability of the lever about an axistransverse to the axis of the control plunger in relation thereto andfurther due to the ability of the control plunger to turn in its valvechamber.

In order to provide a swash plate tilt angle adjustment input, anadjusting lever can be provided and articulated to the control lever, oran axially displaceable control rod can be provided on which isjournalled an axially fixed connector which, in turn, is linked directlyto the control lever by a ball and socket like joint. In the firstembodiment, swash plate adjustment is initiated by a turning motion, inthe second embodiment swash plate adjustment is initiated by a linearmotion in the system to be transmitted upon the control lever. In thelatter 3,618,472 Patented Nov. 9, 1971 case, the axial position of theconnector on the control rod is fixed by a holding disk screwed to theconnector, and having a collar sandwiched between them. The collarpertains to the control rod and defines relative axial position of theconnector on the control rod. The precise axial position of theconnector on the rod results from placement of suitable washers inrelation to collar and connector.

During adjustment by means of turning an adjustment lever, thethree-dimensional movement of the control lever is taken up by the pivotpoint in a ball-and-socket joint, the socket thereof together with theball being disposed to permit displacement thereof in a fork andpertaining to the adjustment lever. However, the fork retains the pivotpoint established by the ball-and-socket joint.

While the specification concludes with claims particularly pointing outand distinctly claiming the subject ma ter which is regarded as theinvention, it is believed that the invention, the objects and featuresof the invention and further objects, features and advantages thereofwill be better understood from the following description taken inconnection with the accompanying drawings in which:

FIG. 1 is a section view into a swash plate, axial piston fluid motor orpump improved in accordance with the invention;

FIG. 2 is a section view along lines I I of FIG. 1, showing details of afirst embodiment of the invention;

FIG. 3 is a vertical section along lines II-II in FIG. 2, and

FIG. 4 can be regarded as a corresponding section view along lines II inFIG. 1 but showing a modified construction as to that section.

Proceeding now to the detailed description of the drawings, there isillustrated a housing 24 journalling a shaft 25 and including paralleloperating pistons 27 which r ciprocate in cylinder barrels such as 26. Aswash plate or tilting plate 1 is mounted on the shaft for rotationtherewith. This fluid device can operate as pump or as motor. Thetilting angle of swash plate 1 is adjusted by means of a control piston2 displaceably disposed in a control cylinder or piston chamber 17. Apiston rod 3 connects plate 1 to piston 2. Adjustment of the tiltingangle serves for the adjustment of the stroke volume or pistondisplacement volume in the axial piston fluid motor or pump.

The control piston 2 is constructed as differential piston, A relativelysmall annular surface 4 of control piston 2 is permanently subjected toa particular hydrostatic pressure. The relatively large circular surface5 on the other side of the piston is selectively subjected to the samepressure or is relieved upon depressurizing chamber 17. The position ofpiston 2 is determined at any instant by the balance of pressure forcesacting on opposite ends of the piston and adjusting same.

In order to avoid dangerous transverse forces and in order to avoidtipping or undesired tilting of piston 2 the permissible angulardeflection of piston rod 3 is maintained rather small. This feature isobtained by selecting a correspondingly large distance between bearingand support points of piston rod 3 on tilting plate 1 and in controlpiston 2, respectively. The connection and pivot point of piston rod 3in control piston 2 is located in the range of piston guidance in thecylinder or chamber 17 (see particularly FIG. 2).

Swash plate 1 is tilted about pivot axis S by means of adjustment ofcontrol piston 2. Upon adjustment, the pivot and linking point and axisat the connection of swash plate 1 and rod 3 describes an arc on whichthere are shown three points, A, B and C, in representation ofparticular adjusting positions. Point A denotes the position of theconnecting point for adjusting the axial piston-cylinder arrangement(27, 26) of the fluid pump or motor for maximum stroke volme. Uponretracting control piston 2, the rod-swash plate linking point is tiltedto assume position B, and here the stroke volume of the pump or motor iszero, as in this position plate 1 is transverse, at right angles, to theaxis of shaft 25. Further retracting of the control piston leads toposition C corresponding to a phase shift by 180 of swash plateoperation because inlet and outlet sides of the axial piston unit havebeen interchanged. In position C there is again maximum stroke volumefor this mode of operation.

The adjustment of the swash plate 1 in accordance with the embodimentsof FIGS. 2, 3 and 4 will be described in the folowing in greater detail.FIGS. 2 and 3 pertain to the same embodiment. FIG. 2 illustrates inparticular a section view wherein the section plane coincides with theplane of operation of the control piston and of the servo valves. Thelinking point of piston rod and swash plate 1, however, can be tiltedout of that plane.

Control fluid is provided through a channel 6 for control of theposition of piston 2. That control fluid may be taken from the mainfluid circuit or from the control circuit or any other suitable sourceor reservoir of pressurized fluid. The control fluid is fed from channel6 to a ring channel 7 to act on piston face 4. Additionally, a duct 8leads from ring channel 7 to a ring channel 9 of a servo valve. Ringchannel 9 is, thus, under pressure of the control fluid. A second ringchannel 10 is connected through a duct 11 to a venting outlet leading tothe tank, i.e., the interior of housing 24 or to any other return pathfor the control fluid at zero pressure. Further fluid conduction isunder control of the servo valve linking these ducts and channels withpiston chamber 17. In particular, a ring chamber 19 may selectively beconnected to channel 10 leading to the venting outlet, or chamber 19 maybe connected to pressurized ring channel 9. Ring channel 19 is connectedto piston chamber 17 via a duct 18. The selectivity of this connectiondepends on the position of a plunger 15.

In the illustrated position of swash plate 1 and of the various controlelements the axial piston-cylinder arrangement of the motor or pump isadjusted for maximum stroke volume (position A). Swash plate 1 isconnected to the control plunger of the servo valve by means of a singlecontrol lever 12. A roll joint 21 establishes articulation betweenplunger 15 and lever 12. An adjusting lever 23 is connected to lever 12by a ball and socket joint estabishing pivot point D (see FIG. 3). Asschematically indicated, lever 23 can be pivotally adjusted by suitablehandle or control knob means, whereby a fork end of the lever 23 turnsin a plane transverse to the plane of FIG. 3 and on an axis transverseto the plane of FIG. 2. As lever 23 turns lever 12 and the point D movein direction E (FIG. 2); control plunger 15 of the servo valve isshifted correspondingly to the right. This is true because the center ofa slidably positioned ball of a ball and socket joint 13 serves as fixedreference point for pivoting. The ball of joint 13 pertains to a pin 14as part of the linkage between swash plate 1 and lever 12.

As control plunger 15 moves to the right its control edge passes thecontrol edge 16 of the valve cylinder establishing communication betweenring chambers 10 and 19, so that the cylinder and piston chamber 17 ofthe control piston (2)-cylinder arrangement is vented through outletduct 11. The conduit path for venting runs particularly from chamber 17via duct 18, ring channel 19 as now connected to ring channel 10, andfrom there to venting duct 11. Thus, chamber 17 depressurizes, and nowthe previously too low pressure force acting on annulus 4 of controlpiston 2 prevails and suffices to shift piston 2 to the right.Accordingly, the swash plate 1 is shifted in direction of point B (seeFIG. 1). Concurrently, the center of the ball of ball and socket joint13 is shifted to the right (FIG. 2). The pivot point D acts as fixedpoint so that double arm lever 12 pulls control plunger 15 of the servovalve to the left and back into its initial position.

The adjustment of swash plate 1 is terminated as soon as the controledge of plunger 15 is receded so that the control edge 16 of the servovalve chamber is blocked again. Now the stroke volume of the axialpistoncylinder arrangement is adjusted in accordance with the newposition of pivot point D, and the position of the latter was adjustedby lever 23.

If adjusting lever 23 is actuated to pivot point D in direction of arrowF, control piston 15 is shifted to the left at first. Thereupon thecontrol edge 20 of the valve chamber is opened. Now a flow path forpressurized control fluid is established, running from ring channel 9across edge 20, ring channel 19, duct 18 to cylinder chamber 17 of theprinciple control piston 2. Hence, chamber 17 will be pressurized. Ascircular area 5 is about twice as large as annulus 4, pressure force onpiston surface 5 soon prevails and shifts control piston 2 to the left.Accordingly, the swash plate 1 is tilted to move towards point A. Byanalogous feed back operation control piston 15 is shifted back to theright until closing control edge 20 (or until the piston 2 has assumedterminal position which limits the tilting angle of swash plate 1).

As was mentioned above, play and slack in a linkage and leverarrangement for returning the control piston is detrimental to theaccuracy of the adjustment. For this reason, the arrangement asdescribed operates with a single lever 12 and there are only two pivotjoints, 13 and 21, thus, solving the aforementioned problem.

In order to compensate changes in length as between the end points ofplunger 15 and piston rod 3 and resulting from the adjustment, ball andsocket joint 13 is provided with a socket bore 22 for the ball. The ballon pin 14 can thus move back and forth in bore 22 of control lever 12.Furthermore, control lever 12 is linked to control piston 15 by means ofroll joint 21 having fixed pivot point and axis in relation to bothelements 12 and 15. Moreover, the pivot axis in joint '21 is transverseto the axis of plunger 15.

During adjustment of the tilting angle of swash plate 1, pin 14 and theball joint 13 outline a section of a circle around tilting axis S whichcircle is in a plane parallel to the direction of control motion ofpiston 2 and of plunger 15. Therefore, lever 12 undergoes athreedimensional motion which must be taken up by a spherical typebearing, so as to avoid locking. The spherical bearing is established inaccordance with a feature of the invention, by permitting concurrentpivoting of control lever 12 about the longitudinal axis of bearing 21as well as rotation of control plunger 15 in its cylinder about itsaxis. As the ball and socket joint linking levers 23 and 12 is slidablydisposed in the fork of lever 23, the threedimensional motion of lever12 is taken up by that linking point.

Turning now to the description of FIG. 4, there is illustrated a secondexample for the swash plate tilting control, using also a servo valvecontrolling a piston drive and being by itself controlled by a plunger15. Again, the pressurized fluid required for operation of controlpiston 2 is fed into duct 6 to be passed on to ring channel 9 of theservo valve via duct 8. Ring channel 10 of the servo valve connects tothe Zero pressure venting and discharge outlet of the system via duct11.

The control plunger 15 is connected to control lever 12 by means of afork 47 and by the roll joint 21. One end of lever 12 is connected toswash plate 1 by means of ball and socket joint 13 comprised of a ballon pin 14 which ball can turn and slide in socket 22 of lever '12. Theother end of lever 12 is connected to a connecting piece or connector 29by means of a ball and socket joint 48. The ball of that joint has abore slidably receiving an end pin 28 of lever 12.

Connector 29 is journalled on a control rod 30 so that the connector canpivot about the longitudinal axis of the rod. The axial position ofconnector 2 9 on rod 30, in longitudinal direction thereon, is a fixedone. For this, control rod 30 is provided with a collar 31. One axialside of collar 31 faces the connector, while on the other side of thecollar there is a holding disk 32. Disk 32 is connected to connector 29by means of bolts 33, and a washer 34 is interposed to determine theprecise axial distance between connector 29 and disk 32. The thicknessof washer 34 is selected in accordance with the thickness of thesandwiched collar 31 so that the collar 31 can rotate within the spacebetween elements 29 and 32 at minimum axial play.

The control rod 30 is axially displaced by forces acting against theforce of a spring 35. Pressurized fluid (control pressure) is fed eitherinto a cylinder chamber 37 via a duct 36 to act on the front face of rod30 or into a cylinder chamber 39 via a duct 38. Chamber 39 contains alsothe spring 35.

The front face of control rod 30 serves as piston upon which may acthydrostatic control pressure. Any particular pressure within aparticular range produces a force capable of balancing spring 35 at aparticular degree of spring compression. Control rod 30 has a centralposition if the two chambers 37 and 39 are both pressure relieved. Inthe central position of rod 30 spring disk 40 bears against cylinder endface 41, while a second spring disk 42 bears against the front face ofan adjustment or trimmer ring 43.

As chamber 37 is pressurized, a particular pressure therein willcorrespond to the then existing bias of spring 35 as threshold. Uponfurther increase of pressure in chamber 37 disk 40 recedes from cylinderend face 41, and rod 30 is shifted to the right and into the positionillustrated in FIG. 4. The spring stroke increases with increasingspring force. Thus, the rod is displaced from central, neutral positionfor a distance which increases with increasing hydrostatic pressure inchamber 37. The cylinder chamber 39 is still depressurized at thatpoint. On the other hand, if chamber 37 is discharged and depressurized,and if chamber 39 is pressurized instead, disk 42 will recede from thefront face of adjusting ring 43, and the control rod is shifted to theleft, out of the position illustrated in FIG. 4.

It should be mentioned that the particular mode of displacement of therod to the left and to the right, to different adjusting positions, hasbeen described here by way of example only, and other modes of motioncontrol can be provided in principle. The displacement of the con; trolrod operates as adjustment of the tilting angle of swash plate 1 in theillustrated poition of control rod 30 the swash plate has a tiltingangle corresponding to maximum piston displacement and stroke volume ofthe pistons 27 in cylinders 26 of the pump or motor. Again, the housingof the axial piston is denoted with 24, journalling drive or drivenshaft 25. The adjusting operation in detail is as follows:

If the control rod 30 is shafted to the left, the center M ofball-and-socket joint 48 is likewise displaced to the left, in directionG. The center of ball-and-socket joint 13 is a fixed pivot point at thattime, so that the control plunger 15 of the servo valve is shifted alsoto the left. Now the control edge of plunger 15 passes over control edge44 of valve chamber 19 and opens a passage between ring channels 19 and10.

Cylinder chamber 17 is vented via duct 18, chamber 19, channel and duct11. As the hydrostatic pressure in chamber 17 collapses, the forceacting on relatively smaller annulus 4 prevails over any residual forceon surface 5, and control piston 2 is shifted to the right. As aconsequence, swash plate 1 is tilted to move towards point B.Concurrently, the center of ball-and-socket joint 13 is shifted to theright. The center M of ball-and-socket joint 48 defines a fixed pivotpoint here so that control plunger of the servo valve is returned to itsinitial position.

Accordingly, the passage via control edge 44 is blocked,

so is the communication between chamber 17 and the venting outlet. Theadjustment of swash plate 1 to a new position of tilting is nowcompleted. The axial piston arrangement of the fluid pump or motor hasnow been adjusted to assume a new stroke volume and corresponding to thedisplacement of control rod 30 from central position to the shaft.

As control rod 30 is shifted to the right, the center M ofball-and-socket joint 48 shifts in direction H. At first, controlplunger 15 is likewise shifted to the right to open passage throughcontrol edge 45 between ring channels 9 and 19. Accordingly, thepressure fluid fed to channel 9 (via 6), is conducted through channel 19and duct 18 into chamber 17, so that full hydrostatic control pressurecan build up therein.

As the circular area 5 of piston 2 is about twice as large as annular 4,force on surface 5 prevails and control piston 2 is shifted to the left.As a consequence, swash plate 1 is tilted in direction A until controledge 45 blocks again passage between channels 6 and 19 or until piston 2has reached terminal position, limiting the tiltingangle 0f swash plate1 accordingly.

As stated above, doubly acting spring 35 places control rod 30 incentral position whenever the two chambers 37 and 39 are depressurized.This position must correspond to a stroke valve zero of the axial pistonarrangement of this swash plate motor or pump. Accordingly, swash plate1 must be adjusted to central position (B) at tilting angle zero forthis control position of rod 30.

In order to trim adjustment position of swash plate 1 to obtain thatcentral position control plunger 15 and fork 47 are provided withthreading 46 to obtain relative positive adjustment between them. Thismay be a self-locking thread to prevent unintended position change.

It is repeated here that the play in any extensive linkage deterioratesaccurately of adjustment as to transmission of linear control action.This problem is solved in the structure as aforedescribed, by connectingcontrol rod 30 to the control lever 12 directly, by means of connector29 and ball-and-socket joint 48. The control lever returns the controlplunger 15 after initial actuation, as piston rod 30 pivots lever 12about pivot point M.

During tilting of swash plate 1, pin 14 and, therefore, ball-and-socketjoint 13 outlines a circle about tilting axis G. The resultingthree-dimensional motion of the control lever 12 is taken up by aspherical bearing. Special bearing support is established by permittingconcurring pivoting of lever 12 about the longitudinal axis of rolljoint 21 and by permitting control plunger 15 to turn in the valvechamber. As the three-dimensional motion of lever 12 is also operativeas longitudinal displacement between lever 12 and the pivot point 48, itis also necessary to permit such axial displacement as between lever end28 and the ball of joint 48. Additionally, connector 29 can pivot aboutthe longitudinal axis of rod 30, thus, compensating three-dimensionallever movement in cooperation and the universal joint like adjustment ofball-andsocket joint 48. The length compensation as between connector 29and lever 12 results from shifting of lever end 28 in the ball of joint48. As it can be seen further from FIG. 4, the connector turns in aplane transverse to the plane of tilting motion, the latter plane beingtransverse to axis S. This way, the compensatory turning of connectorhas practically no influence on the tilting.

The invention is not limited to the embodiments described above but allchanges and modifications thereof not constituting departures from thespirit and scope of the invention are intended to be included.

I claim:

1. A device for infinite adjustment of the stroke volume in a pressurefluid, swash plate, axial piston motor or pump, the swash plate coupledto a control piston for tilting the swash plate about a first axis,there being a servo valve controlling the Position of the piston, andbeing controlled by a plunger, the improvement comprising:

a control lever articulated to the swash plate and connected to theplunger by means permitting pivoting of the control lever relative tothe plunger about an axis transverse to said first axis, the plungerdisposed for rotation about its own axis; and

adjusting means linked to the control lever for pivoting the controllever about its point of articulation to the swash plate for changingthe position of the plunger to obtain valve operation, and establishinga pivot point for the control lever upon resulting piston displacementwhereby the plunger is returned to its previous position concurring withturning about its axis and change in angle relation to the controllever.

2. A device for infinite adjustment of the stroke volume in a pressurefluid, swash plate, axial piston motor or pump comprising:

a piston-cylinder arrangement, the piston thereof connected to the swashplate for adjusting the tilting angle thereof in dependence upon therelative position of the piston;

a servo valve, including a plunger, the servo valve controlling thefluid in the piston-cylinder arrangement;

a control lever for directly conecting the plunger to the swash platefor providing stabilizing feed back;

means for pivotally linking the swash plate to the control lever;

a roll joint pivotally linking the plunger to the control lever, forpivoting about an axis transverse to the axis of the plunger, theplunger permitted to turn in the servo valve chamber about its axis toobtain spherical bearing support for the lever; and adjusting meansconnected to the control lever to determine an initial position of theplunger for initiating adjusting of the swash plate tilt angle by thepiston as controlled by the servo valve.

3. A device as in claim 2, the adjusting means coupled to the controllever for pivoting the control lever about a pivot point established bypivotally linking the swash plate to the control lever, and includingmeans establishing a particular pivot point for the control lever uponchange of the relative position of the piston, said established pivotpoint relatively movable to the axis of the roll joint transversethereto upon pivoting of the control lever about said established pivotpoint.

4. A device as in claim 3, there being a ball and socket jointconnecting the adjusting means to the control lever for establishingsaid particular pivot point and constructed to permit lineardisplacement of the particular pivot point in relation to the adjustingmeans of the lever.

5. A device as in claim 3, the control lever articulated to the swashplate by a ball and socket joint, the socket thereof permitting lateraldisplacement of the ball in a direction having an angle to the tiltingplane of the swash plate.

6. Device as in claim 2, the adjusting means including an adjustinglever articulated to the control lever.

7. Device as in claim 6, there being a ball-and-socket joint forarticulating the control lever to the adjusting lever and establishing apivot point slidably disposed on the adjusting lever, for taking upthree dimensional movement of the control lever upon change of tiltingangle by operation of the control piston.

8. A device as in claim 7, the adjusting lever being a turning forkreceiving and slidably positioning a ball and socket joint, the controllever connected to the ball thereof.

9. Device as in claim 2, the adjusting means including an axiallymovable control rod;

a connector journalled on the rod;

means inhibiting axial displacement of the connector on the rod; and

a ball-and-socket joint linking directly the connector with the controllever.

10. Device as in claim 9, the inhibiting means including a collar on therod, a holding disk secured to the connector, the collar being disposedbetween the connector and the disk, there being at least one distancedefining washer in between the connector and the disk.

11. Device as in claim 9, the ball of said joint having an apertureslidably receiving one end of the control lever for articulatedlylinking the lever to the connector.

References Cited UNITED STATES PATENTS 2,578,561 12/1951 Lagardelle91-506 3,139,006 6/1964 Budzich 91506 3,463,087 8/1969 Grant 91-506CARLTON R. CROYLE, Primary Examiner J. J. VRABLIK, Assistant ExaminerUS. Cl. X.R. 417222

